1. Field of the Invention
This invention relates generally to an information recording/reproducing method and apparatus and to a transmission medium for use therein and, more particularly, relates to an information recording/reproducing method and apparatus and to a transmission medium that is able to search a desired track reliably despite employing a simplified structure.
2. Description of the Background
FIG.7 shows the principal elements of a conventional optical disc device, in which an optical disc 2 is rotated at a pre-set speed by a spindle motor 1. A pickup 3 associated with the head mechanism illuminates laser light radiated from an enclosed laser diode via an objective lens 4 to the optical disc 2 for recording/reproducing the information. A sled motor 6, is configured for transporting the pickup 3 via a gear 7 along a sled guide rod 5 in the radial direction of the optical disc 2.
A servo amplifier 8 generates focussing error signals, tracking error signals, and traverse signals from an output signal of the pickup 3 to output the thus generated signals to a servo processor 9. The traverse signal is a signal generated by comparing the tracking error signal with a zero level as a reference level.
The servo processor 9 processes the focussing error signals in a pre-set fashion to route the processed focussing error signals via a focussing drive amplifier 10 to the pickup 3 to drive the objective lens 4 in the correct focussing direction. The servo processor 9 also processes the tracking error signals in a pre-set fashion to send the processed signals to the pickup 3 via a tracking drive amplifier 11 to drive the objective lens 4 by a tracking actuator to make small adjustments in the tracking direction. The servo processor 9 also is responsive to the output signals from the servo amplifier 8 to generate a sled drive signal from the voltage signals of the low range component and sends this sled drive signal via a sled drive amplifier 12 to the sled motor 6 to transfer the pickup 3 via a gear 7 along a sled guide rod 5 in the radial direction of the optical disc 2. The servo amplifier 8 also controls the spindle motor 1 to control the rotation of the optical disc 2.
FIG. 8 represents a circuit structure mainly for the tracking servo and the sled servo. The tracking error signals are fed to a first low boost filter (LBF) 23 and outputted via a high-range, phase-lead, high boost filter (HBF) 36, an adder 32, and an amplifier 33. A speed verifying unit 34 detects a rising edge and a falling edge of an input traverse signal and verifies the transfer speed of the pickup 3 using the edge interval and outputs a result of the decision to a tracking drive controller 35. During ordinary reproduction, neither the speed verifying unit 34 nor the tracking drive controller 35 is used. During fine search, however, the tracking drive controller 35 is responsive to a signal from the speed verifying unit 34 to generate pulses for driving the pickup 3 in the direction toward the outer rim of the disc or to generate pulses for driving the pickup 3 in the direction toward the inner rim of the disc and outputs the so-generated pulses to the adder 32.
The tracking drive output is again fed as a sled error signal to a second low boost filter 37 and subsequently fed to a sled drive controller 39. This signal is amplified by an amplifier 40 to drive the sled motor as a sled motor drive output signal, which drives the pickup 3 in the direction toward the outer rim or toward the inner rim of the disc along the sled guide rod 5.
Referring to the timing chart of FIGS. 9A-9E, the operation for performing a fine search will be explained. Fine search means the operation of jumping the pickup 3 track-by-track in the direction toward the outer rim or toward the inner rim of the disc to transfer the pickup 3 a pre-set number of tracks, such as from 10 to 1000 tracks, in order to search for the desired track. In the fine search, the pickup moves first and then the sled follows.
As an example of operation, if a controller in the form of a micro-computer, not shown, issues a command for doing a fine search toward outer rim side tracks for a pre-set number of tracks, the tracking drive controller 35 outputs a tracking drive kick pulse, shown in FIG. 9D, to effect a jump of the objective lens 4 by one track in the direction toward the outer rim of the disc. It is assumed that a signal of positive polarity is a signal for transferring the objective lens 4 in the direction toward the outer rim of the optical disc 2, and that a signal of negative polarity is a signal for transferring the objective lens 4 in the direction toward the inner rim of the optical disc 2. Therefore, in this example, a kick pulse of positive polarity is output from the tracking drive controller 35 and is routed via the adder 32 and the amplifier 33 to the tracking drive amplifier 11 and thence to the pickup 3. This causes the objective lens 4 of the pickup 3 to jump by one track in the direction toward the outer rim of the optical disc 2. Similar operations are carried out in succession until a jump of the pre-set number of tracks is achieved.
In such case, the tracking error signal output by the servo amplifier 8 is varied sinusoidally each time the pickup performs a track jump, as shown in FIG. 9A. The traverse signal, generated by comparing the tracking error signal to the zero level reference, is a rectangular signal having a rising edge or a falling edge at the zero-crossing point of the tracking error signals. The speed verifying unit 34 detects the rising and falling edges of the traverse signal and generates edge detection signals, as shown in FIG. 9C. The speed verifying unit 34 also measures an interval T of the edge detection signals to check whether this interval T is larger than a pre-set reference value, that is, to check the period or speed, of the fine search. If the interval T is larger than a reference value, that is, if the fine search speed is slower than the reference speed, the speed verifying unit 34 outputs a signal of, for example, positive polarity and if the interval T is smaller than the reference value, that is, if the fine search speed is faster than the reference speed, the speed verifying unit 34 outputs a signal of negative polarity.
The tracking drive controller 35 generates tracking drive kick pulses, based on results of the decision from the speed verifying unit 34, in meeting with the fine search direction. Since the fine search direction in this case is toward the outer rim of the disc, the tracking drive controller 35 generates a tracking drive kick pulse of positive polarity if the signal from the speed verifying unit 34 is of positive polarity. On the other hand, if the signal from the speed verifying unit 34 is of negative polarity, it generates a tracking drive kick pulse of negative polarity.
Thus, if the fine search speed is slower than the reference speed, the objective lens 4 is kicked or jumped by the tracking pulse in the direction toward the outer rim of the optical disc 2, that is, in the fine search direction. Conversely, if the fine search speed is faster than the reference speed, the objective lens 4 is fed with a tracking drive kick pulse to move it in the direction toward the inner rim of the optical disc 2. It should be noted that, because the objective lens 4 is continuously jumping in the direction toward the outer rim of the optical disc 2 as the disc is being played back, by this tracking drive kick pulse in the direction toward the inner rim of the disc the objective lens 4 is braked against driving in such direction, with the result that servo is applied so that the fine search speed will be a pre-set reference speed, without actually being jumped in the direction toward the inner rim.
Meanwhile, with the pickup 3 being halted on the sled guide rod 5, if the objective lens 4 is shifted gradually in its position from the center towards the outer rim of the optical disc 2, the pickup 3 needs to be moved in the same direction as the objective lens 4, because the objective lens 4 cannot be moved beyond its movable range. That is, the pickup 3 must catch up to the objective lens 4. Thus, the tracking drive controller 35 outputs a control signal to the sled drive controller 39 only during a time when accelerating pulses are generated for movement in the radial direction on the disc. At this time, the sled drive controller 39 generates sled drive kick pulses, as shown in FIG. 9E, that are fed to the sled motor 6 via amplifier 40 and sled drive amplifier 12. This causes rotation of the sled motor 14 to transport the pickup 3 via gear 7 in the direction toward the outer rim of the optical disc 2. It suffices if, at this time, the gain of the amplifier 40 is adjusted so that the objective lens 4 will not be offset significantly from the center within the pickup 3.
The fine search comes to a close when the above-described operations are repeatedly performed to effect the track jump operation over the pre-set number of tracks.
In a conventional optical disc device, the sled motor 6 is typically designed as a DC motor. Thus, the conventional optical disc device is increased in size and difficult to design with a small size, because of the provision of the sled motor 6 as a DC motor along with the gear 7.
Recently, attempts have been made to use a stepping motor to reduce the size of the optical disc device. If the stepping motor is used, the gear 7 is redundant.
A characteristic of a stepping motor is that the amount of rotation of the motor is determined solely by the number of pulses inputted to the motor. Thus, it becomes impossible to adjust the gain, as in the case of the DC motor, to prevent the objective lens from becoming offset from the center within the pickup.
Also, if the fine search operation is interrupted, due to flaws on the disc, for example, it has not been possible with the conventional mechanism employing the conventional DC motor to transport the head a distance corresponding to the initial target movement number of tracks.
Thus, it is an object of the present invention to realize a fine search operation in a sled movement mechanism employing a stepping motor.
It is another object of the present invention to enable the head to be transported to a position close to the target track, by exploiting characteristics of the stepping motor in realizing correct transporting distance, even if the search is interrupted.
For resolving the above problem, the present invention in one aspect records or reproduces the information for a disc, in which, with the use of a head supported by a supporting member for movement along the radius of the disc, the head is moved a prescribed distance in the direction along the radius of the disc, the distance over which the head is moved along the radius of the disc is detected and head movement by a head driver is controlled in accordance with the detected distance.
In another aspect, the fine search is enabled by a sled motor mechanism employing a stepping motor. Also, a pickup can be transported to the vicinity of a target, even on interruption of the fine search. The apparatus includes a speed detection unit that detects a fine search speed from an interval between a decaying edge and a rising edge of a traverse signal generated based on zero-crossings of tracking error signals and a tracking drive controller that generates tracking drive kick pulses of such a polarity as to give a constant fine search speed. When a traverse counter has counted the edges in an amount corresponding to the distance of one step of micro-step driving of the stepping motor, it controls a sled drive controller to transport the pickup by one step in a direction along the radius of the disc, which is a so-called fine search direction.